1. Technical Field
This invention relates in general to electroplating and etching, and in particular to an apparatus and method for controlling the thickness, uniformity, and composition of electroformations.
2. Background Art
In electroplating, a thin film of metal or alloy is deposited on a workpiece that is submerged in an electrolytic bath. The workpiece acts as a cathode when connected to the negative terminal of a power supply. An anode is similarly submerged and connected to the positive terminal of the power supply. Electrical current flows between the anode and the cathode through the electrolyte, and metal is deposited on the workpiece through an electrochemical reaction.
It is highly desirable to deposit the metal on the workpiece at a uniform thickness and composition, especially with electrical component workpieces. However, electroplating is relatively complex and various naturally occurring forces may degrade the process. In particular, the current or flux path between the anode and cathode should be relatively uniform to ensure uniform deposition. In addition, as metal ions are depleted from the electrolyte, its uniformity is decreased and must be adjusted to avoid degradation of the process. Furthermore, debris is generated in the chemical reactions that also can degrade the process.
In the prior art, uniformity and consistency in electroplating has been achieved by several methods. In U.S. Pat. No. 5,312,532, an electroplating system circulates solution between horizontally-disposed anodes and workpiece cathodes in multiple compartments. The workpiece cathodes are located on the floors of the compartments and the anodes are located above the cathodes. A horizontally-oriented paddle is reciprocated in a horizontal plane between the terminals and slightly above the cathode workpieces to improve performance of the system. Each of the paddles comprises an opposed pair of elongated elements having a triangular prismatic or semi-cylindrical shape. The flat side of one of the elements moves just above the workpiece in parallel relation.
In U.S. Pat. No. 5,516,412, an electroplating system circulates solution between a vertically disposed anode and a workpiece cathode. The workpiece cathode is mounted on a wall of system and the anode is on an opposite wall. A vertically-oriented paddle is reciprocated in an upright position between the terminals immediately adjacent to the cathode workpiece to improve performance of the system. In this design, the paddle comprises an opposed pair of elongated prisms wherein the flat side of one of the prisms moves just above the workpieces in parallel relation. Although these systems are workable, an improved electroplating system is desirable.
An electroplating system circulates solution between an anode and a workpiece mounted to a cathode. A shaped agitation paddle is reciprocated immediately adjacent to the cathode workpiece to improve performance of the system. The paddle is an elongated prism or other elongated shape having a generally flat side that is parallel to the workpiece. The flat side has a fluid port connected to a pump. The solution may be pumped with either positive pressure to force the solution against the surface of the workpiece, or negative pressure to draw the solution away from the surface of the workpiece. In an alternate embodiment, the cathode workpiece is rotated in the solution above an anode with a stationary, shaped paddle in between them.